An airbag which has been quickly increasing in its installing rate in recent years as one of the safety parts for cars is used for such a purpose that, in car collisions, a sensor perceives the shock, gas of high temperature and high pressure is generated from an inflator and the airbag is quickly developed by the gas whereby the collision of the bodies or, particularly, the heads of a driver and a passenger to steering wheel, windshield, door glass, etc. is prevented and protected. In recent years, airbags for cars have been developed in their practical use not only for a driver seat and a passenger seat but also for knee airbags, side airbags, curtain airbags, etc. and installment of a plurality of airbags is now becoming common.
As regions and numbers of the installed airbags are increasing, there has been an increasing demand for making the weight and the size of an airbag system lighter and more compact and each of the parts of the system has been designed with a target of making the weight lighter and the size more compact. In view of such a background, airbags have been investigated for a plan of using a fabric where the yarn of small fineness is used or for a plan of reducing the type of elastomer of a coating textile and the coating amount.
For example, fineness of a filament used in a coated fabric for airbags is becoming finer from 940 dtex to 470 dtex and, in recent years, there has been a change to a fabric using the filaments where fineness is 350 dtex.
Furthermore, an elastomer resin which is coated to a coated fabric for airbags has been also changed from chloroprene to silicone resin. The coating amount has been changed from 90 to 120 g/m2 to 40 to 60 g/m2 and, in recent years, has been reduced to 25 to 40 g/m2. Although package ability of the airbag has been significantly improved by these means, the package ability has not reached satisfactory level. Therefore, improved package ability and weight reduction by further reduction of the coating amount are desired.
On the other hand, although a coated fabrics applied with synthetic rubbers or resins such as silicone for airbags such as side airbags, curtain airbags, and knee airbags for which an internal pressure retention performance is particularly required are mainly used, the resin film is easy to break and extremely low air permeability is difficult to maintain due to extreme reduction of a resin amount existed on the surface when the resin amount is reduced to 20 g/m2 or less.
With regard to a coated fabric for airbags where the coating weight of silicone resin is reduced, there is a disclosure for an airbag where elastomer is unbalancedly present in terms of a coating thickness ratio of not less than 3.0 in the knotted area of the textile to 1.0 of textile yarn area which constitutes the textile (see Patent Document 1). Although the package ability of the airbag is improved, the resin film is easy to break in the state that the resin is unevenly distributed as described above when the resin amount is adjusted to 20 g/m2 or less. As a result, it is difficult to satisfy the low air permeability to the airbags for which an internal pressure retention performance is particularly required.
There is also a disclosure for a coated fabric for airbags where not less than 90% of the outer circumstances of the cross sections of warp and weft positioned at the resin-coated surface of the synthetic fiber textile are surrounded by said resin and the coating weight of the resin is not more than 20 g/m2 (see claim 2 of Patent Document 2). Although adhesion between the fabric and the resin is improved by impregnating the resin, the resin film is easy to break in a similar manner due to a thin resin film existed on the textile surface. As a result, it is difficult to satisfy the low air permeability to the airbags for which an internal pressure retention performance is particularly required.